Method for the production of plates

ABSTRACT

The invention relates to a method for the production of plates from continuously cast slabs. Immediately after the continuously cast bar has solidified and as soon as its marginal zone has reached a mean temperature of 800* to 1000* C while the core zone is still of higher temperature, a continuously cast bar is shaped in a preliminary one-step shaping process in which primarily the core zone is shaped. After shearing to length, the slabs are cooled, re-heated to rolling temperature and shaped in a multistep rolling process proper wherein essentially the marginal zones of the slabs are subjected to shaping so that finally a uniform degree of shaping is achieved over the total cross section of the slabs. By this new method it becomes possible to produce plates with a cross section of 50 to 100 mm by using continuously cast slabs whose initial thickness does not exceed 300 mm.

United States Patent 11 1 Schoffmann [451 Jan. 16, 1973 1541 METHOD FOR THE PRODUCTION OF 3,554,269 1/1911 11mm et al. 164/76 x PLATES 3,580,032

Inventor: Rudolf Scholtmann, Linz, Austria Assignee: Vereiniate Oster-reichische Eisenund Stahlwerke Aktiengesellschaft, Linz, Austria Filed: April 27, 1970 Appl. No.: 32,459

Foreign Application Priority Data May 9, 1969 Austria ..A 4444/69 References Cited UNITED STATES PATENTS Cofer et al 1 65/76 Tarmann et al. Tarmann et a1. Pearson ..29/527.7

5/1971 Stone et al ..l64/76 X Primary Examiner-J. Spencer Overholser Assistant Examiner-John E. Roethel Attorney-Brumbaugh, Graves, Donohue & Raymond 5 7] ABSTRACT The invention relates to a method for the production of plates from continuously cast slabs. Immediately after the continuously cast bar has solidified and as soon as its marginal zone has reached a mean temperature of 800 to 1000C while the core zone is still of higher temperature, a continuously cast bar is shaped in a preliminary One-step shaping process in which primarily the core zone is shaped. After shear ing to length, the slabs are cooled, re-heated to rolling temperature and shaped in a multi-step rolling process proper wherein essentially the marginal zones of the slabs are subjected to shaping so that finally a uniform degree of shaping is achieved over the total cross section of the slabs. By this new method it becomes possible to produce plates with a cross section of 50 to 100 mm by using continuously cast slabs whose initial thickness does not exceed 300 mm.

2 Claims, No Drawings METHOD FOR THE PRODUCTION OF PLATES The invention relates to a method for the production of plates from continuously cast slabs.

It is of advantage to use slabs produced according to the continuous casting method as processing material in the rolling mill because theirthickness need not even amount to about 300 mm so that substantially less shaping work is necessary when small final dimensions are produced. In order to 'fully benefit from the economic advantages of continuous casting the determination of the dimensions of the final product should be based on an initial thickness of the slabs of less than 300 mm.

It has been known that rolled products show satisfactory technological characteristics'only when the cast product receives at least a fourfold, preferably at least a sixfold shaping so that the as-cast structure is destroyed and one may be certain that thematerial is transformed not only in the marginal zones but also in the core of the rolled product to obtain a uniform as-rolled structure. When deciding the degree of shaping one has to consider that a total of a sixfold shaping may include only a threefold shaping in the core of the rolled product. In other words, the degree of shaping must be as high as possible because the marginal zones which are turned towards the rolls, are always shaped to a greater extent than the core zone.

When using continuously cast slabs having an initial cross section of about 200 to 300 mm and if a six fold shaping is desired, it will, in general, be possible only to produce plates with a final thickness of about 35 to 50 mm. It is very difficult to produce from continuously cast slabs plates of more than 50 mm, for example of up to about 100 mm, with satisfactory quality. If the normal rolling technique were employed such plates would be insufficiently shaped in the core and thus the mechanical properties would be wanting both in longitudinal and transverse direction.

The invention is aimed at avoiding these drawbacks and difficulties and, in a method for the production of plates from continuously cast slabs, wherein these slabs are heated to rolling temperature and shaped in several steps, resides in that the cast bar prior to being shorn to length, immediately after its solidification in the continuous casting process, is shaped in one step as soon as its marginal zone has reached a mean temperature of 800 to 1000C while the core zone is still of a higher temperature, preferably of a temperature that is higher by atleast 100C.

In this one-step preliminary shaping process it is primarily the core zone that is shaped, while the marginal zone remains substantially unshaped. Only later, after shearing to length, cooling, re-heating of the slabs, in the multi-step rolling process proper, the marginal zone is shaped so that finally a uniform degree of shaping is achieved over the total cross section. Preferably the core zone which amounts to from about one fifth to about one third of the total bar cross section is subjected to a 1.3 to 2.5 fold shaping during the one-step shaping process of the bar and the entire cross section of the continuously cast bar is reduced by 7 to percent.

The one-step shaping process according to the invention suitably takes place by means of a customary shaping stand arranged after the secondary cooling zone of the continuous casting plant, Thus, the first shaping is carried out by exploiting the sensible heat of the bar. Owing to the fact that the resistance to shaping. increases with declining temperature and increases greatly at temperatures below about 900C, the core zone of a bar having a high temperature will be shaped to a greater extent than its marginal zones having relatively low temperatures; in other Words, the core zone will be shaped thoroughly while the marginal zones will hardly be shaped at all. After this first shaping process the surface may be cleaned, if desired, before the slab is introduced into the pusher-type furnace where it is heated to rolling temperature.

The multi-step second rolling process takes place in known manner on a customary train of rolls at normal rolling temperatures; i.e. the slabs to be rolled are uniformly heated. What has been described in the introduction will happen now in this second rolling process, i.e. the core zone is shaped to a lesser degree than the marginal zones. Seeing, however, that the initial thickness of the continuously cast slab was reduced by the first shaping process in the stand of rolls arranged after the continuous casting plant, the second shaping process further improves the shaped condition of the core zone or center. The second rolling process thus serves to equalize the different degree of shaping resulting from the first rolling process. An examination of the cross section of the plate shows that shaping has been effected in a highly uniform manner. Plates produced according to this method have a thickness of about 50 to 100 mm and boast improved technological characteristics although shaping has been effected only to a three or fourfold degree.

It has already been proposed to cast and roll continuously. Thus, a continuous furnace, a descaling device and a Sendzimir-rolling stand together with all necessary post-positioned rolling mill devices have been provided immediately succeeding a continuous casting plant in order to produce sheets directly from the cast bar. However, this process is not suitable for the production of thick plates; nor would a direct and onestep shaping process amount to any progress over the art, i.e. the core would still be shaped to a lesser degree than the marginal zone.

According to another proposal tending to improve the quality of cast bars the bar is shaped before it has solidified completely, i.e. when it has still a liquid core. This process, however, is suitable only for billets.

The method according to the invention is illustrated by the following examples:

Example 1 illustrates the shaping of a bar having an initial cross section of 210 mm which is shaped to a final cross section of 75 mm in two steps, namely in a preliminary shaping process after complete solidification of the bar and in a rolling process after heating the continuously cast slat to rolling temperature.

marginal zone core zone M= mm C=70 mm (=l9% reduction of cross section) cross section after the second rolling process D"=75 mm M"+C"+M"=D" M"=25 mm C"=25 mm Shaping of the M'/M"=2,6 C'/C"=1 ,6 individual zones total degree of shaping M/M"=2,8 C/C"=2 in the first and second rolling process Example 2 illustrates the shaping of a bar with an initial cross section of 250 mm, which, as described in Example 1, is first subjected to a preliminary shaping process, whereupon the continuously cast slab is heated to rolling temperature and then secondary shaping is effected in a rolling process; the final cross section amounts to 100 mm marginal zone core zone initial cross section D=250 mrn M+C+M=D cross section after the first rolling process D'=2 10 mm M+C'+M'=D shaping of the individual zones mean degree of shaping in the first rolling process M=l00 mm C=50 mrn (=16 reduction of cross section) cross section after the second rolling process D"=l00 mm u u iv n shaping of the individual zones mean degree of shaping in the second rolling process total degree of shaping in the first and second rolling process means degree of total shaping in the first and second shaping processes Example 3 illustrates the reduction of a bar with an initial cross section of 200 mm to a final cross section of 65 mm marginal zone M core 20l1 initial cross section D=200 mm M+C+M=D cross section after the first rolling process D'=l85 mm M'+C'+M=D' shaping of the individual zones mean degree of shaping in the first rolling M=80 mm C=40 mm The data given in the Examples are based on simplified assumptions: The cross section of the bar or of the slab respectively is regarded to be composed of three parts, and each of the three zones (marginal, core, marginal zone) is assumed to be shaped independently of the others. Obviously, this will not happen in actual practice; rather, there will be a gradual transition from one zone to the other.

As becomes obvious from Example 1, the core zone received a 1.75 fold shaping in the first rolling process while the marginal zones received only a 1.08 fold shaping. In the second rolling process it is the other way round: the core zone received a 1.6 fold shaping while the marginal zones received a 2.6 fold shaping. Finally, however, the finished plate shows a uniform 2.8 fold shaping throughout its cross section.

Example 2 illustrates the shaping of a bar whose core zone C was assumed to amount to not more than onefifth one of the entire diameter D. After the first shaping process the core zone shows a 2.5 fold shaping, while the degree of shaping of the marginal zones is extremely low with 1.05. In the second shaping process the marginal zones received a 2.35 fold shaping, while the core zone received only a 1.05 fold shaping. The

plate finally has a degree of core shaping of 2.63 as compared to a marginal zone shaping degree of 2.47, which equally does not represent a great deviation from the average 2.5 fold total shaping; this plate, too, has excellent technological properties.

Example 3 illustrates the shaping of a bar whose core zone C was assumed to amount to not more than about one-fifth of the total diameter D; also, it was assumed that the entire reduction of the cross section achieved in the first rolling process amounts to only 7.5 percent. The core zone receives a 1.33 fold shaping in the first rolling process, while the marginal zones receive a l .03 fold shaping only. In the second rolling process the marginal zones are shaped to a substantially higher degree than the core zone so that finally a plate is obtained showing in total a 2.67 fold shaping of the core zone and a 3.2 fold shaping of the marginal zone which again does not greatly deviate from the average total degree of shaping of 3.08. This shows that already at a relatively lower degree of total shaping in the first rolling process a considerable improvement in the quality of the plates is afforded by the method according to the invention as compared to plates manufactured according to the conventional rolling technology.

The method according to the invention makes it possible to use continuously cast slabs for the production of thick plates, whereas until now it had been necessary for this purpose to use heavy slabs having a thickness of more than 600 mm.

What I claim is: 1. A method for the production of plates from continuously cast bars comprising continuously casting a bar subjecting said bar to a one-step shaping operation when the mean temperature of the marginal zone is in the range from about 800 to 1000C, the temperature of the core zone is greater than the temperature of the marginal zone, and the core zone comprises about one-fifth to one-third of the cross section of the bar, shaping said core zone about 1.3 to 2.5 fold by said one-step shaping operation,

is in the range from about 800 to 1000C and the temperature of the core zone :is greater, reducing the cross section of the bar about 7 percent to 20 percent by said one-step shaping operation, shearing said bar to form individual slabs and allowing said slabs to cool, re-heating said slabs to rolling temperature, and subjecting said slabs to a rolling process to form plates. 

1. A method for the production of plates from continuously cast bars comprising continuously casting a bar subjecting said bar to a one-step shaping operation when the mean temperature of the marginal zone is in the range from about 800* to 1000*C, the temperature of the core zone is greater than the temperature of the marginal zone, and the core zone comprises about one-fifth to one-third of the cross section of the bar, shaping said core zone about 1.3 to 2.5 fold by said one-step shaping operation, shearing said bar to form individual slabs and allowing said slabs to cool, re-heating said slabs to rolling temperature, and subjecting said slabs to a rolling process to form plates.
 2. A method for the production of plates from continuously cast bars comprising continuously casting a bar subjecting said bar to a one-step shaping operation when the mean temperature of the marginal zone is in the range from about 800* to 1000*C and the temperature of the core zone iS greater, reducing the cross section of the bar about 7 percent to 20 percent by said one-step shaping operation, shearing said bar to form individual slabs and allowing said slabs to cool, re-heating said slabs to rolling temperature, and subjecting said slabs to a rolling process to form plates. 